1. Field of the Invention
The present invention relates to a novel styrene-based resin composition. More particularly, it is concerned with a styrene-based resin composition which is excellent in a physical balance; for example, has a high Izod impact strength, and a high drop-weight impact strength, and further excellent in gloss and stiffness, and thus is suitable as a material for production of office automation (OA) devices, home electric applicances, sheets, and so forth.
2. Background Information
In recent years, for housings of TV sets, a styrene-based resin composition excellent in a well balanced manner in physical properties, such as gloss, Izod impact strength, drop-weight impact strength, and stiffness has been increasingly demanded.
For the purpose of improving impact resistance of a styrene-based resin, the blending of a rubber-like polymer with polystyrene, and polymerization of styrene in the presence of a rubber-like polymer to cause graft polymerization of part of styrene onto the rubber-like polymer and polymerization of the remaining styrene into polystyrene, thereby forming a so-called rubber-modified polystyrene resin composition in which the rubber-like polymer/styrene graft polymer and the polystyrene are in a mixed state have been employed on a commercial scale.
It is known that use of a conventional diblock-type styrene-butadiene copolymer or a tapered block-type styrene-butadiene copolymer as the above rubber-like polymer increase the impact strength. For example, impact resistant polystyrene using a full block-type styrene-butadiene copolymer as the rubber-like polymer (Japanese Patent Application Laid-Open No. 165413/1988 and Japanese Patent Application No. 311530/1987), an impact resistant polystyrene using a tapered block-type styrene-butadiene copolymer (Japanese Patent Application Laid-Open Nos. 71549/1977 and 48317/1988), and so forth are disclosed.
These impact resistant polystyrenes, however, are not always sufficiently satisfactory in all of physical properties such as gloss, Izod impact resistance, drop-weight impact strength, and stiffness.
It is also known that in a rubber-modified polystyrene resin composition, the usual rubber-like polymer is dispersed in the styrene-based polymer in the form of particles, and that the particle size is in a close relationship with impact resistance, stiffness, and gloss. Namely, as the particle size is smaller, stiffness and gloss are higher. On the contrary, as the particle size is decreased, impact resistance is reduced, and above a certain limit, the effect of improving impact resistance is substantially lost.